The effect of low-temperature conditions on the electrochemical polymerization of polypyrrole films with high density, high electrical conductivity and high stability

High-quality polypyrrole-hexafluorophosphate (PPy-PF6) films with high density ( similar to 1.4 g/cm(3)), high conductivity ( > 300 S/ cm for unstretched film) and high electrochemical stability are obtained reproducibly by galvanostatic polymerization at low-temperature conditions. The optimal polymerization current density of J(p) = 0.02-0.05 mA/cm(2) was obtained at the polymerization temperature of T-p= -40 degrees C. The surface morphology of the film sensitively varies depending upon the properties of electrode and its surface conditions. The transport measurements characterize the high-density PPy-PF6 film as a disordered metal close to the boundary of disorder induced metal-insulator (M-I) transition. The X-ray diffraction measurements suggest that partially crystalline structure of PPy-PF6 film is related to the transport properties. The uniaxial stretching induces an increase of the conductivity up to similar to 930 S/cm in a direction parallel to stretching as well as the anisotropy of conductivity. The comparative studies of thermogravimetric analysis (TGA), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) for PPy-PF6 films prepared at room-temperature and low-temperature conditions show that the latter exhibit better thermal stability as well as electrochemical stability under long oxidative polarization. (C) 1999 Elsevier Science S.A. All rights reserved.